1. Field of the Invention
The present invention relates to an ink jet head employed for an ink jet recording apparatus that discharges ink droplets to record images on a recording medium.
2. Related Background Art
Conventionally, an ink jet recording apparatus is known that records characters and images on a recording medium by employing an ink jet head that includes a plurality of nozzles from which ink is discharged. The type of ink jet head frequently employed includes, as a single unit, multiple nozzles, pressure generators and ink guide holes, and an ink jet head wherein multiple arrays of nozzles and pressure generator arrays are provided is well known. FIG. 12 is a schematic cross-sectional view of an example ink jet head unit wherein two nozzle arrays are arranged with their positions shifted relative to each other. FIG. 13 is a plan view of a head chip block, and FIG. 14 is a schematic cross-sectional view of the entire ink jet head.
As shown in FIG. 12, a plurality of parallel grooves 3 are formed in piezoelectric ceramic plates 2 and 5, and are separated by side walls. One longitudinal end of each groove 3 is extended to one end face of the piezoelectric ceramic plate 2 or 5, while the other end is not extended to the other end face, so that the depth of the grooves 3 is gradually reduced.
Ink chamber plates 7 and 10, which form common ink chambers 32 and 33 that communicate with the shallow side ends of the grooves 3, are connected to the sides of the piezoelectric ceramic plates 2 and 5 where the grooves 3 are opened. Thus, two head chips are provided. The piezoelectric ceramic plates 2 and 5 of the two head chips are bonded together to obtain a head chip block 50.
A nozzle plate 15 is adhered to the end face of the head chip block 50, and nozzle holes 16 are formed in the nozzle plate 15 at locations corresponding to the grooves 3. The nozzle plate 15 and the head chip block 50 are fixed together by a head cap 17, and electrodes that are formed on the piezoelectric ceramic plates 2 and 5 are connected to a drive circuit board by a flexible board.
Furthermore, ink flow paths 34 and 35, for supplying ink to the common ink chambers 32 and 35, are secured to the two ink chamber plates 7 and 10, and ink guide joints 39 and 40 are formed in the center of the ink flow paths 34 and 5 in order to introduce ink. Further, pressure relaxing units 41 and 42 are connected to the ink guide joints 39 and 40 to absorb the pressure fluctuation that occurs during printing. In addition, filters 36 and 37 are fixed to the ink flow paths 34 and 35 to prevent foreign substances from entering the nozzle holes 16.
In the thus arranged ink jet head, ink is supplied to the individual grooves 3 via the pressure relaxing units 41 and 42 and the ink flow paths 34 and 35, and when a predetermined drive field is applied, the volumes of the grooves 3 are changed and ink in the grooves 3 is discharged from the nozzle holes 16. That is, the ink flow path 34 and the path along which ink is supplied to the ink chamber plate 7 and the piezoelectric ceramic plate 2 forms a set. Similarly, the ink flow path 35 and the path along which ink is supplied to the ink chamber plate 10 and the piezoelectric ceramic plate 5 forms a set. These sets are independent of each other, i.e., two ink flow paths are provided for the laminated head chip block 50.
However, according to the conventional ink jet head, the ink flow path 34 and the path along which ink is supplied to the ink chamber plate 7 and the piezoelectric ceramic plate 2 form a set, while the ink flow path 35 and the path along which the ink is supplied to the ink chamber plate 10 and the piezoelectric ceramic plate 5 form another set, and these two sets are independent of each other. Thus, two ink flow paths are required for one head chip block 50, and accordingly, two pressure relaxing units must respectively be provided. Therefore, the size of the ink jet head in the direction of thickness is increased, and the weight can not be reduced. Moreover, the number of parts is increased, and the manufacturing cost is increased.
When an ink jet recording apparatus is to be provided by mounting a plurality of such ink jet heads, the attachment area is extended, and also, the weight is increased.